According to Feachem et al. (1980), the persistence of fecal pathogens in the environment can be summarized as follows:

IN SOIL

Survival times of pathogens in soil are affected by soil moisture, pH, type of soil, temperature, sunlight, and organic matter. Although fecal coliforms can survive for several years under optimum conditions, a 99% reduction is likely within 25 days in warm climates (see Figure 7.1). Salmonella bacteria may survive for a year in rich, moist, organic soil, although 50 days would be a more typical survival time. Viruses can survive up to three months in warm weather, and up to six months in cold. Protozoan cysts are unlikely to survive for more than ten days. Roundworm eggs can survive for several years.

The viruses, bacteria, protozoa, and worms that can be passed in human excrement all have limited survival times outside of the human body. Let's take a look at their survival times when deposited raw into soil (refer to Tables 7.8 through 7.12).

SURVIVAL OF PATHOGENS ON CROPS

Bacteria and viruses cannot penetrate undamaged vegetable skins. Furthermore, pathogens are not taken up in the roots of plants and transported to other portions of the plant.30 However, pathogens can survive on the surfaces of vegetables, especially root vegetables. Sunshine and low air humidity will promote the death of pathogens. Viruses can survive up to two months on crops but usually live less than one month. Indicator bacteria may persist several months, but usually only last less than one month. Protozoan cysts usually survive less than two days, and worm eggs usually last less than one month. In studies of the survival of Ascaris eggs on lettuce and tomatoes during a hot, dry summer, all eggs degenerated enough after 27 to 35 days to be incapable of infection.31

Lettuce and radishes in Ohio sprayed with sewage inoculated with Poliovirus I showed a 99% reduction in pathogens after six days; 100% were eliminated after 36 days. Radishes grown outdoors in soil fertilized with fresh typhoid-contaminated feces four days after planting showed a pathogen survival period of less than 24 days. Tomatoes and lettuce contaminated with a suspension of roundworm eggs showed a 99% reduction in eggs in 19 days and a 100% reduction in four weeks. These tests indicate that if there is any doubt about pathogen contamination of compost, the compost should be applied to long-season crops at the time of planting so that sufficient time ensues for the pathogens to die before harvest.

PATHOGEN SURVIVAL IN SLUDGE AND FECES/URINE

Viruses can survive up to five months, but usually less than three months in sludge and night soil. Indicator bacteria can survive up to five months, but usually less than four months. Salmonellae survive up to five months, but usually less than one month. Tubercle bacilli survive up to two years, but usually less than five months. Protozoan cysts survive up to one month, but usually less than ten days. Worm eggs vary depending on species, but roundworm eggs may survive for many months.

Table 7.8

SURVIVAL OF ENTEROVIRUSES IN SOIL

Soil Type

pH

% Moisture

Temp. (°C)

Days of Survival(less than)

Sterile, sandy

7.5

10 - 20%

3 - 10

130 - 170

10 - 20%

18 - 23

90 - 110

5.0

10 - 20%

3 - 10

110 - 150

10 - 20%

18 - 23

40 - 90

Non-sterile, sandy

7.5

10 - 20%

3 - 10

110 - 170

10 - 20%

18 - 23

40 - 110

5.0

0 - 20%

3 - 10

90 - 150

10 - 20%

18 - 23

25 - 60

Sterile, loamy

7.5

10 - 20%

3 - 10

70 - 150

10 - 20%

18 - 23

70 - 110

5.0

10 - 20%

3 - 10

90 - 150

10 - 20%

18 - 23

25 - 60

Non-sterile, loamy

7.5

10 - 20%

3 - 10

110 - 150

10 - 20%

18 - 23

70 - 110

5.0

10 - 20%

3 - 10

90 - 130

10 - 20%

18 - 23

25 - 60

Non-sterile, sandy

7.5

10 - 20%

18 - 23

15 - 25

Source: Feachem et al., 1980

Table 7.9

SURVIVAL TIME OF E. HISTOLYTICA PROTOZOA IN SOIL

Protozoa

Soil

Moisture

Temp. (°C)

Survival

E. histolytica

loam / sand

Damp

28 - 34

8 - 10 days

E. histolytica

soil

Moist

?

42 - 72 hours

E. histolytica

soil

Dry

?

18 - 42 hours

Source: Feachem et al., 1980

Table 7.10

SURVIVAL TIME OF SOME BACTERIA IN SOIL

Bacteria

Soil

Moisture

Temp. (°C)

Survival

Streptococci

loam

?

?

9 - 11 weeks

Streptococci

sandy loam

?

?

5 - 6 weeks

S. typhi

various soils

?

22

2 days - 400 days

Bovine tubercule bacilli

soil & dung

?

?

less than 178 days

Leptospires

varied

varied

summer

12 hours - 15 days

Source: Feachem et al., 1980

Table 7.11

SURVIVAL TIME OF POLIOVIRUSES IN SOIL

Soil Type

Virus

Moisture

Temp. (°C)

Days of Survival

Sand dunes

Poliovirus

dry

?

Less than 77

Sand dunes

Poliovirus

moist

?

Less than 91

Loamy fine sand

Poliovirus 1

moist

4

90% reduction in 84

Loamy fine sand

Poliovirus 1

moist

20

99.999% reduction in 84

Soil irrigated w/ effluent, pH=8.5

Polioviruses 1, 2 & 3

9 - 20%

12 - 33

Less than 8

Sludge or effluent, irrigated soil

Poliovirus 1

180mm total rain

-14 - 27

96 - 123 after sludge applied

-14 -27

89 - 96 after effluent applied

190mm total rain

15 - 33

less than 11 days after sludge or effluent applied

Source: Feachem et al., 1980

Table 7.12

SURVIVAL TIME OF SOME PATHOGENIC WORMS IN SOIL

Worm

Soil

Moisture

Temp. (°C)

Survival

Hookworm larvae

Sand

?

room temp

less than 4 months

Soil

?

open shade, Sumatra

less than 6 months

Soil

Moist

Dense shade

9 - 11 weeks

Mod. shade

6 - 7.5 weeks

Sunlight

5 - 10 days

Soil

Water covered

varied

10 - 43 days

Soil

Moist

0

less than 1 week

16

14 - 17.5 weeks

27

9 - 11 weeks

35

less than 3 weeks

40

less than 1 week

Hookworm ova (eggs)

Heated soil with night soil

water covered

15 -27

9% survival after 2 weeks

Unheated soil with night soil

water covered

15 - 27

3% survival after 2 weeks

Roundworm ova

Sandy, shaded

25 - 36

31% dead after 54 days

Sandy, sun

24 - 38

99% dead after 15 days

Loam, shade

25 - 36

3.5% dead after 21 days

Loam, sun

24 - 38

4% dead after 21 days

Clay, shade

25 - 36

2% dead after 21 days

Clay, sun

24 - 38

12% dead after 21 days

Humus, shade

25 - 36

1.5% dead after 22 days

Clay, shade

22 - 35

more than 90 days

Sandy, shade

22 - 35

less than 90 days

Sandy, sun

22 - 35

less than 90 days

Soil irrigated with sewage

?

less than 2.5 years

Soil

?

2 years

Source: Feachem et al., 1980

Table 7.13

PARASITIC WORM EGG DEATH

Eggs

Temp. (°C)

Survival

Schistosome

53.5

1 minute

Hookworm

55.0

1 minute

Roundworm

-30.0

24 hours

Roundworm

0.0

4 years

Roundworm

55.0

10 minutes

Roundworm

60.0

5 seconds

Source: Compost, Fertilizer, and Biogas Production from Human and Farm Wastes in the People's Republic of China, (1978), M.G. McGarry and J. Stainforth, editors, International Development Research Center, Ottawa, Canada. p. 43.